Review `getTransitionDurationFromElement` to implement multiple durations

Created by: alpadev

getTransitionDurationFromElement only respects the duration of one (the first) CSS transition. If there are multiple transitions defined and one that takes longer (which isn't the first one) setTimeout (used in the executeAfterTransition function) might finish too early. (This shouldn't be the case with our defaults from what I can tell.)

Originally posted by @alpadev in https://github.com/twbs/bootstrap/pull/33845#discussion_r639396189